> > > > I don't think this is a problem because the instruction bytes stream > > has irrelevant bytes in it anyway. In the test attached I verify that > > it receives an flds instruction in userspace that was emulated in the > > guest. In the stream that comes through insn_size is set to 15 and > > the instruction is only 2 bytes long, so the stream has irrelevant > > bytes in it as far as this instruction is concerned. > > As an experiment I added[1] reporting of the exit reason using flag 2. On > emulation failure (without the instruction bytes flag enabled), one run > of QEMU reported: > > > KVM internal error. Suberror: 1 > > extra data[0]: 2 > > extra data[1]: 4 > > extra data[2]: 0 > > extra data[3]: 31 > > emulation failure > > data[1] and data[2] are not indicated as valid, but it seems unfortunate > that I got (not really random) garbage there. > > Admittedly, with only your patches applied ndata will never skip past > any bytes, as there is only one flag. As soon as I add another, is it my > job to zero out those unused bytes? Maybe we should be clearing all of > the payload at the top of prepare_emulation_failure_exit(). > Clearing the bytes at the top of prepare_emulation_failure_exit() sounds good to me. That will keep the data more deterministic. Though, I will say that I don't think that is required. If the first flag isn't set the data shouldn't be read, no? > Footnotes: > [1] https://disaster-area.hh.sledj.net/tmp/dme-581090/ > > dme. > -- > Music has magic, it's good clear syncopation.
